Calcium-phospholipid-phosphate complexes have been isolated from young animal bones and shown to be present in greatest proportion in those areas where calcification is being initiated. These same complexes have been shown to cause hydroxyapatite formation from metastable calcium phosphate solutions. The object of this study is to learn more about the factors controlling lipid-induced calcification by: (1) further characterizing the nature and amount of complexed lipids in normally mineralizing tissues; (2) characterizing the complexed lipids of pathological calcification; (3) investigating the molecular structural features of the Ca-PL-PO4 complex that cause it to nucleate hydroxyapatite; (4) in-vitro studies to determine what factors might prevent, or control Ca-PL-PO4 complex formation. Lipid extraction techniques previously developed will be used to isolate and separate the complexed lipids from the total lipids. Complex composition will be determined by standard chemical analysis. Where required total lipid composition will be determined by chromatographic means. Structural features will be elucidated by measuring infrared spectra, wide-angle x-ray scattering by thin films, small -angle x-ray scattering of lipid emulsions, and electrophoretic patterns. The factors affecting hydroxyapatite nucleation by lipids will be evaluated in solutions shown to be metastable with respect to apatite by chemical analyses of both the changes in solution composition and the nature of the solid.